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Intracellular pH (pHi)

From original article: "Intracellular pH (pHi) is the measure of...pHi of 6.8-7.1)". There is also pH variation across different organelles, which can span from around 4.5 to 8.0. The pH within a particular organelle is tailored for its specific function. For example, phagocytes and lysosomes have a relatively low internal pH. pHi can be measured in a number of different ways, and pHi is closely regulated in order to ensure proper cellular function, controlled cell growth, and normal cellular processes.

Methods for Measuring Intracellular pH

There are several ways in which intracellular pH (pHi) can be measured. The main ways in which pHi can be measured is with a microelectrode or dye that is sensitive to pH, or with nuclear magnetic resonance techniques.

Microelectrode

The microelectrode method for measuring pHi consists of placing a very small electrode into the cell’s cytosol by making a very small hole in the plasma membrane of the cell. Since the microelectrode has fluid with a high H+ concentration inside, relative to the outside of the electrode, there is a potential created due to the pH discrepancy between the inside and outside of the electrode. From this voltage difference, and a predetermined pH for the fluid inside the electrode, one an determine the intracellular pH (pHi) of the cell of interest.

Fluorescence Spectroscopy

Another way to measure Intracellular pH (pHi) is with dyes that are sensitive to pH, and fluoresce differently at various pH values. This technique, often referred to as fluorescence spectroscopy, consists of adding this special dye to the cytosol of a cell. By exciting the dye in the cell with energy from light, and measuring the wavelength of light released by the photon as it returns to its native energy state, one can determine the intracellular pH of the given cell.

Nuclear Magnetic Resonance

In addition to using pH-sensitive electrodes and dyes to measure pHi, Nuclear Magnetic Resonance (NMR) spectroscopy can also be used to quantify pHi. NMR, typically speaking, reveals information about the inside of a cell by placing the cell in an environment with a potent magnetic field. Based on the ratio between the concentrations of protonated, compared to deprotonated forms of phosphate compounds in a given cell, the internal pH of the cell can be determined. Additionally, NMR may also be used to reveal the presence of intracellular sodium, which can also provide information about the pHi.

Summary of Measurement Methods

Overall, all three methods have their own advantages and disadvantages. Using dyes is perhaps the easiest and fairly precise, while NMR presents the challenge of being relatively less precise. Furthermore, using a microelectrode may be challenging in situations where the cells are too small, or the intactness of the cell membrane should remain undisturbed.

How Intracellular pH is maintained

From original article: "Intracellular pH is typically lower...and pHi decreases." Since biological cells contain fluid that can act as a buffer, pHi can be maintained fairly well within a certain range. Cells adjust their pHi accordingly upon an increase in acidity or basicity with the help of CO₂ or HCO₃^- sensors present in the membrane of the cell. These sensors can permit H+ to pass through the cell membrane accordingly, allowing for pHi to be interrelated with extracellular pH in this respect.

Additional Information

From original article: "Lymphocytes maintain ... USA."